1. Field of the Invention
The present invention relates to an electrode catheter for intervention purposes, such as a cardiac pacemaker, neurostimulator, ICD electrode, or EP catheter. The term “electrode catheter” is to be understood as all types of elongate implants which comprise at least one wire enclosed in the elongate body of the implant and running largely insulated from the patient therein using at least one surrounding medium, which is in direct or indirect electrical contact with the surrounding medium (e.g., body tissue) in proximity to the distal end. In addition to the above-mentioned types, for example, electrophysiological diagnostic catheters, ablation catheters, and pacemaker electrodes may also be cited.
2. Description of the Related Art
Electrode catheters of this type are known to have an elongate body having a distal end and a proximal end. At least one electrode pole is provided in the area of the distal end, which is typically used for discharging intervention pulses or perceiving cardiac, nerve, or brain signals. This electrode pole is designed, for example, as a tip electrode situated directly on the distal end, as a ring pole placed at a distance therefrom, or as a shock electrode. The intervention pulses discharged via this pole are the pacemaker pulses of a cardiac pacemaker or neurostimulator, a high-voltage pulse in the case of a defibrillator, or an ablation energy pulse in the case of an ablation device, for example.
An insulated supply line runs to this electrode pole in the electrode body. Furthermore, such electrode catheters usually have further electrode poles, which are generally thus referred to, via which the supply line may come into electrical contact with tissue. A ring electrode pole of a bipolar electrode or an EP catheter is to be cited as an example. Furthermore, an electrode sheath, which encloses the at least one supply line, is provided in the electrode body for insulating the supply line.
In recent years, magnetic resonance diagnostic devices have gained significantly in importance because of their examination methodology, which is gentle to patients, non-invasive, and completely free of pain and side effects. Typical electrode catheters display the problem that electrode catheters of this type strongly heat the tissue in magnetic resonance diagnostic devices under the influence of the electromagnetic radiation generated thereby because of electromagnetic induction and the discharge of the induced energy in the area of their contact surface(s) to the tissue. The reason for this is particularly in the solid, metallic supply lines to the electrode poles, which act as antennas and in which, because of their insulation, the antenna currents induced by high-frequency (HF) fields may only be dissipated into the body electrolytes at the electrode poles, which form the electrical interface to the tissue. The cited HF fields operate, for example, in an operating frequency range of 64 MHz for a 1.5 Tesla MR tomograph. Because extremely strong heating of the tissue may occur in proximity to the electrode poles, the access to magnetic resonance diagnostic devices is typically blocked to wearers of cardiological and neurological intervention devices, such as cardiac pacemakers, neurostimulators, or defibrillators. Electrophysiological examinations and interventions, such as ablations, are also not possible in MR devices.
To prevent or minimize the hazardous heating of the body cells, the maximum antenna currents must be limited or reduced. Known solutions suggest discrete components for this purpose, which act as a band-stop filter or as a low-pass filter and thus limit the longitudinal current of the antenna for the frequencies of interest or, in other words, increase the longitudinal resistance of the antenna. Other solutions suggest capacitors which are connected in parallel to the insulation and thus dissipate the antenna current.
In this regard, for example, U.S. Pat. No. 6,944,489, US 2003/0144720, US 2003/0144721, US 2005/0288751 A1 (and the simultaneously published parallel publications US 2005/0288752 A1, US 2005/0288754 A1, and US 2005/0288756 A1, which have essentially the same wording) are cited.
US 2006/0009819 A1 discloses a cardiac pacemaker having an elongate electrode which is connected to a pulse generator connector. A passive lossy circuit is provided, which is electrically connected between a distal section of the electrode supply line and a high-frequency grounded surface. The passive lossy circuit has a high-frequency impedance which is approximately equal to a characteristic impedance of the electrode in its implanted state in the body. The reflection of incident waves is thus minimized at the terminals of the lossy circuit and their energy is intentionally dissipated here. The passive lossy circuit also acts as a low-pass filter, because of which the electrode is functional in normal operation of the cardiac pacemaker.
The known solutions have the disadvantage that discrete components complicate the production and thus make it costly. In addition, such discrete components reduce the reliability and long-term stability of electrode catheters, which is particularly disadvantageous if they are provided as long-term implants. Finally, discrete components, such as inductors and resistors, require a certain overall size if they are provided for high-current applications, such as defibrillators and HF ablation. This is contrary to the attempts to design an implant as especially small and slim.